Please check the Service Routing Technote, that is available from https://support.arubanetworks.com/Documentation/tabid/77/DMXModule/512/EntryId/7961/Default.aspx
My personal advice would be to just use the management port, and only use the data port after you read and understood the Technote. ClearPass works fine with just a single interface, and having just one interface keeps your design simple in most cases.
In short, when you enable both ports, all outgoing traffic will originate from the data-port, unless it is local for the management port subnet, or if there is a management route that can be set on the command-line only.